Voltage amplifying apparatus



Nov. 11,1941. D, w. EXNER 2,251,982

VOLTAGE AMPLIFYING APPARATUS Filed Fb. 1a, 1940 Iii" I I 7 I v '7 WITNESSES: INVENTO'R 6Z4 pobaldwfxoerr 7*? I BY I ATTORNEY Patented Nov. 11, 1941 UNITED STATES PATENT OFFICE Donald W. Exncr, Forest Hills, Pa assignor to Westinghouse, Electric 4; Manufacturing Company, East Pittsburgh, Pennsylvania Pa., a corporation of Application February 16, 1940, Serial No. 319,318

Claims. (Cl. 171-312) My invention relates to electronic apparatus and control circuits therefor and is particularly applicable to electronic regulators having a direct current amplifier between a voltage measuring device and a controlled source of supply of 5 energy to the field'winding of a generator or similar device.

In such equipment, the amplifier tubes ordinarily require a more or less fixed negative direct current bias on the control grid so that the operation of the tube will occur normally in the region of negative grid voltage. This causes the amplifier to operate without drawing grid current so that the tube may be controlled by a low energy source. This arrangement also minimizes plate current losses.

In the past, it has been customary to provide a separate source of unidirectional potential such as a battery or a rectifier and filter to obtain this negative grid bias. Such arrangen'i'ents require a source of energy separate from that supplying the plate power for the amplifier. Since this negative bias voltage has heretofore been of 'a substantially fixed value, variations in vacuum tube characteristics have caused a marked variation in the value of the regulated voltage, since the tube output is not determined solely by grid potential but also largely by tube characteristic.

It is an object of my invention to provide an electronic regulator system employing a direct current grid controlled amplifier, together with means for developing a negative grid bias component of voltage therefor without the necessity for providing a source of grid bias potential separate from that supplyi the anode current of the amplifier.

Another object of the invention is the provision of means for controlling an amplifying tube of the character indicated by. a grid bias that is a function of tube current to thereby compensate the tube activity for changing tube characteristics. v

It is a more specific object of the invention to provide an electronic system employing an amplifier tube, the operation of which is determined in part by the voltage drop across a resistor through which the "anode current of the tube passes and, in part, by the voltage dropacross a resistor that varies as a function of the regulated quantity and which two operating forces act in opposition.

It is a further object of the invention to limit the opposing efiects of the tube component voltage parts above referred to so that a small driving voltage only is required from the voltage measuring device controlling the amplifier .tube.

Other objects and advantages of the invention will be apparent from the following description of a preferred embodiment of the invention, reference being made to the single figure oi' the drawing, which illustrates circuits and apparatus comprising one embodiment of the invention.

In the drawing, a three-phase circuit is illustrated comprising main circuit conductors I, 2.

and 3 that are connected to be supplied with energy from an alternating current generator 4 having -a field winding 5. The phase-sequence of these conductors is assumed to be 1--23 in the following description. The field winding is supplied with energy from rectifier units supplied from circuit conductors I, 2 and 3 through an anode transformer having a three-phase primary winding 8 connected to the circuit and a secondary winding I connected-in zigzag Y, and from the outer terminals of which conductors 8, 9 and I0 are connected to anodes ll, i2 and I2, respectively, of rectifier tubes l4, l5 and IS. The rectifier tubes l4, l5 and iii are provided with cathodes ll, i8 and I9, respectively, that are connected by means of conductors 22 and 23 to the secondary winding 24 of a filament transformer, the primary winding 25 of which is connected to the circuit conductors I and 3. The circuit for supplying energy to the field winding 5 extends from the cathodes ll, l8 and I! of the tube rectifiers through conductors 22 and 23, the secondary winding 24 of the filament transformer, conductor 28, field winding 5, conductor 21 to the neutral point 28 of the anode transformer winding 1 and through the three branch circuits represented by conductors 8, 9 and It to the anodes ll, l2,,and I3 of tubes l4, l5 and it. The grid control circuit for the tubes l4, l5

and it extends from the cathodes ll, l8 and through conductors 22 and 23, the filament transformer winding 24, conductor 26 to'a sliding contact member 3i that engages a selected point along a resistor 32, that is connected to a positive conductor 33 of. a source of unidirectional potential, through resistor 34, conductor 35 to the neutral point36 of a Y-connected v winding 31 constituting the secondary of phaseshifting transformer, through the branches of the Y and conductors 38, 39 and 4! to grids 42,

43 and 44, respectively, of tubes l4, l5 and ii. The phase-shifting transformer is also provided with a three phase primary winding 45 connected to the circuit conductors l, 2 and 3. l

The resistor 22 serves as a bleeder resistor connected in series with a resistor 46 between the positive conductor 33 and a negative conductor 41 or a unidirectional voltage source. An amplifier tube 48 is provided having an anode 49 connected to the end of resistor 34 remote from the conductor 33, and a cathode 5| connected to a junction point 52 between the bleeder resistor 32 and the resistor 45 so that the tube current flows between conductors 33 and 41 in shunt relation to the resistor 32 and in series relation with the resistor 45. The tube 48 is provided with a heater element 53 for heating the cathode 5|, which heater element is connected through a filament transformer 54 to conductors and 2 of the generator output circuit. The tube 48 is also provided with a screen grid 55 and a control grid 55. The screen grid 55 is connected through a resistor 51 to the positive conductor 33 of the previously mentioned unidirectional voltage source. The grid circuit for the control grid 55 extends from cathode 5| through the resistor 45, conductor 41, resistor 59, a potentiometer resistor 62 and from a selected point thereon determined by the position of the contact member 53 through conductor 54 and resistor 55, to the control grid 55.

A detector tube 56 is provided for controlling a circuit extending from the positive terminal 33 to the negative terminal 41 of the previously mentioned unidirectional voltage source, and comprises an anode 51 connected to the conductor 33 and a cathode 58 that is connected through a network including a resistor 59 and condenser 12 inparallel circuit relation, the two previously mentioned resistors 52 and 59 in series relation, and a resistor 13 that is connected in parallel circuit relation to the previously named portion of the network. The tube 65 is of the diode hot filament type in which the conductivity of the tube is determined by the temperature of the cathode 68 which is connected by a filament transformer having a secondary winding 14 and a primary winding 15 to line circuit conductors 2 and 3 for heating the cathode 58 in accordance with the voltage of the power circuit conductors.

If the system is in operation and the voltage supplied by the generator 4 is at the desired value, the current flowing from conductor 33 to conductor 41 through the detector tube 55, which is a measure of the voltage of the line conductors of the power circuits 2 and 3, will be just sufiicient to establish the correct bias on the grid 55 of the amplifier tube 45 to maintain the desired current flow through the rectifier tubes |4, I5 and I5 and the field winding 5 of the generator 4 for maintaining the desired voltage on the power circuit conductors for the existing conditions on the system. If the voltage of the power circuit conductors 2 and 3 increases above the desired value, this increased potential is impressed through the filament transformer windings 15 and 14 and the filament 58 of the detector tube 55, thus increasing the current fiow through the tube and through the network including resistors 62 and 55, to increase the voltage drop between the points 53 and conductor 41 which decreases the negative bias of the grid 55 and causes the amplifier tube 45 to become more conducting, thus causing an increase in the flow of current from the positive conductor 43 through resistor 34, to the tube anode 45 and from the tube cathode 5| through resistor 45 to the negative conductor 41. The increase in current flow through the resistor 34 increases thenegative bias on the grids 42, 43 and 44 of the tube rectifiers |4, I5 and IS in the above traced grid control circuit, causing the rectifier tubes l4, l5 and I5 to pas les current to the field winding 5 and thus to decrease the voltage of the generator 4. At the same time, the increase in current fiow through the tube 48 increases the voltage drop across the resistor 45 to slightly increase the negative bias on the control grid 55.

. It will be noted that the resistor 45, connected thus causing the voltage drop across the resistor to vary to a less degree than the variations in the plate and screen current of the tube so that for a change in conductivity of the detector tube 55, the voltage drop between conductor 41 and the contact member 53 will vary to a greater degree than the voltage drop across the resistor 45. This prevents the voltage drop across the resistor 45 from too greatly bucking the voltage drop between conductor 41 and point 45 so that a smaller change in voltage applied to the measuring device 55 is required to effect a correction in the value of the regulated voltage from its desired value. If the voltage of the power circuit I, 2, 3 decreases below its desired value, the opposite result will be effected, namely, the voltage applied to the filament cathode 58 of the voltage measuring tube 55 will be reduced, causing the conductivity of the tube to be decreased and the fiow of current through the tube and the network including resistors 52 and 59 to be likewise decreased, thus increasing the negative bias on the grid 55 of the amplifier tube 43 and decreasing the fiow of current through this tube. The decrease in the flow of current through the tube 48 likewise decreases the current flow through resistors 34 and 45 in series with the tube, the former decreasing the negative bias on the grids of tubes |4, I5 and I6 to cause them to supply a greater current to the field winding 5 of the generator 4, and the latter decreasing the drop across the resistor 45.

Since the voltage drop across the resistor 45 changes in part a the result of changing current fiow through the amplifier tube 48, variation in this component of grid bias voltage partlally overcomes variations in the component of grid bias voltage between conductor 41 and the contact 53 constituting the tap on the potentiometer resistor 52. It the initial characteristic of the amplifier tube 48 should change, for example, due to partial loss of emission from the cathode, thus causing a decrease in plate and screen current thereto, the resulting decrease in the component oi! grid bias voltage developed across the resistor 45 would cause a net change in grid voltage in a direction to increase the conductivity ofthe tube 45. By a proper selection of the various resistors included in the circuits, this effect may be made quite pronounced so that the regulated voltage cannot vary appreciably from the desired value as a result of changes in the tube characteristics. As

this efiect is increased, however, a greater drivotherwise than by the scope greater variation in the voltage drop between conductor 41 and the contact member 63 for the same change in generator voltage. Sufllcient current is permitted to pass through the bleeder resistor 32 to limit the bucking effect of the voltage, drop across the resistor 46 and thus make the circuit more sensitive to changes in the regulated voltage than it otherwise would be.

Many modifications in the circuits and apparatus illustrated and described will occur to those skilled in the art and I do not wish to be limited of the appended claims.

I claini as my invention:

i. In an electronic regulator for controlling the characteristic of an electric circuit, in combination, an electric circuit to be regulated, grid controlled electronic means for governing said characteristic, 9. source of unidirectional volt'age energy, an amplifier tube connected to saidsource, a resistor connected in series with saiding included in the grid circuit of said grid controlled electronic means and the other of said resistors being included in the grid circuit of said amplifier tube, a second resistor included in the grid circuit of said amplifier tube and connected to said unidirectional voltage source in a direction to develop a voltage component in the grid control circuit of said amplifier tube that is of opposite polarity to that developed across the first named resistor oi the grid circuit, a detector tube responsive to the said controlled characteristic connected in series with said last named resistor, and a circuit between the terminals of tube between the tube and the positive terminal of said source and a resistor connected in series terminal of said source, one of said resistors being included in the grid circuit of said grid controlled electronic means and the other of said with said tube between the tube and the negative 1 resistors being included in the grid. circuit of said amplifier ,tube, a second resistor included in the grid circuit of said amplifier tube and connected to said unidirectional voltage source in with said last named resistor.

2. In an electronic regulator for controlling the characteristic of an electric circuit, in comsaid source including a resistor in the grid ciracteristic, a source of unidirectional voltage energy, an amplifier tube connected to said source, a resistor connected in series with said tube between the tube and the positive terminal of said source and a resistor connected in series with said tube between the tube and the negative terminal of said source, one of said resistors being included in the grid circuit of said grid controlled electronic means and the other of said resistors being included in the grid circuit or said amplifier tube, a second resistor included in the grid circuit or said amplifier tube and connected to said unidirectional voltage source in a direction to develop a voltage component in the grid control circuit of said amplifier tube that is of opposite polarity to that developed across the first named resistor of the grid circuit, a detector tube responsive .to the said controlled characteristic bination, an electric circuit to be regulated, grid controlled electronic means for governingsaid characteristic, a source of unidirectional voltage energy, an amplifier tube connected to said tive terminal of said source, one oi-said resistors being included in the grid circuit of said grid controlled electronic means and the other oi said resistors being included in the grid circuit of" said amplifier tube, a secondresistor included inthe grid circuit or said amplifier tube and connected to said unidirectional voltage source in a direction to develop a voltage componentiin the grid control circuit of said amplifier tube that is or opposite polarity to that developed across the first named resistor or the grid circuit; a de-.

tector tube responsive to the said, controlledv characteristic connected in series with said last source, a resistor connected in series with said tube between thetube and the positive terminal 01' said source and a resistor connected in series with said tube between the tube and the negative terminal of said source, one of said resistors being included in the grid circuit of said grid controlled electronic means and the other or said resistors being included in the grid circuit of said amplifier tube, a second resistorincluded in the grid circuit of said amplifier tube, and connected to said unidirectional-voltage source in a direcnamed resistor, and a circuit connection in shunt to said amplifier tube and in series with the first named resistor of said amplifier tube grid circuit.

3f1n an electronic regulator tor controlling the characteristic 0! an electric circuit, in combina,

source, a resistor connected in series with said tube between the tube and the positive terminal or saidsource and a resistor connected in series withsaidhibebetweenthetubeandthcnegativc -terminaioissidscurce,oneotsaidresistonbetion to develop a voltage component in the grid' control circuit or said amplifier tube that is of opposite polarity to that developed across the resistor, and a circuit'between the terminals of said source including a bleeder resistor-and the first named resistor in the grid circuit oi! said amplifier tube, the bleeder resistor having such value that its current is considerably-greater than the current from the amplifier tube,

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